OBJECTIVES: 1. The development of a method (now completed) for measuring regional lung expansion as a continuous function of inspired volume. The method utilizes (a) radioactive xenon as a tracer gas whose concentration is monitored by six external scintillation detectors, (b) a mathematical procedure derived for a continuous computation of the fraction of inspired gas entering a given zone per unit volume of that zone, and (c) a computer system for calculating time derivatives of regional tracer concentration and lung volumes. 2. The method is intended to be for practical application to untrained normal subjects and patients with various diseases. 3. The method is to be applied to: a. The development of technology required to study the influence of regional airway resistance and pulmonary compliance on regional lung expansion. b. The study of chronic obstructive lung disease and restrictive diseases of the lung and chest wall. c. A comparison of regional vs. total airway resistance and their response to therapy in asthma and emphysema. d. The study of alpha1 antitrypsin deficiency in individuals without evidence of pulmonary disease. e. Characterize the localization and rate of change of the pathologic process in chronic bronchitis and emphysema.